English

On $r$-wise $t$-intersecting uniform families

Combinatorics 2024-10-01 v1

Abstract

We consider families, F\mathcal{F} of kk-subsets of an nn-set. For integers r2r\geq 2, t1t\geq 1, F\mathcal{F} is called rr-wise tt-intersecting if any rr of its members have at least tt elements in common. The most natural construction of such a family is the full tt-star, consisting of all kk-sets containing a fixed tt-set. In the case r=2r=2 the Exact Erd\H{o}s-Ko-Rado Theorem shows that the full tt-star is largest if n(t+1)(kt+1)n\geq (t+1)(k-t+1). In the present paper, we prove that for n(2.5t)1/(r1)(kt)+kn\geq (2.5t)^{1/(r-1)}(k-t)+k, the full tt-star is largest in case of r3r\geq 3. Examples show that the exponent 1r1\frac{1}{r-1} is best possible. This represents a considerable improvement on a recent result of Balogh and Linz.

Keywords

Cite

@article{arxiv.2409.19344,
  title  = {On $r$-wise $t$-intersecting uniform families},
  author = {Peter Frankl and Jian Wang},
  journal= {arXiv preprint arXiv:2409.19344},
  year   = {2024}
}
R2 v1 2026-06-28T19:00:31.812Z